1. Field of the Invention
This invention relates to a liquid catalyst component, a catalyst system containing the same and a process for producing ethylene-.alpha.-olefin copolymers, using the catalyst system. More particularly, this invention relates to a liquid catalyst component, a catalyst system containing the same and a process using the catalyst system for producing ethylene-.alpha.-olefin copolymers having a narrow composition distribution and being excellent in weather resistance, colorizability, corrosion resistance, dynamic properties and solution polymerization performances.
2. Description of the Prior Art
As a process for producing ethylene-.alpha.-olefin copolymers, the method using the so-called Ziegler-Natta catalyst comprising a compound of a transition metal belonging to Group IV-VI of the periodic table and a compound of an organometal belonging to Group I-III of the periodic table is widely known generally.
On the other hand, from the viewpoint of practical properties, ethylene-.alpha.-olefin copolymers are desired to have a narrow composition distribution. Thus, they are industrially produced by the use of a catalyst system comprising a vanadium compound such as VCl.sub.3, VOCl.sub.3, and the like and an alkylaluminum halide.
Although such a catalyst system gives an ethylene-.alpha.-olefin copolymer having a narrow composition distribution, the catalyst system has a low polymerization activity at high temperatures, and hence it is low in productivity. Further, it has problems of coloration, deterioration in weathering and corrosion caused by the residual vanadium and chlorine, and the formed copolymer must be made free from ash sufficiently in order to prevent these problems. Further, if ethylene is copolymerized with an .alpha.-olefin having a large carbon number with this type of catalyst system, the resulting ethylene-.alpha.-olefin copolymer is so low in molecular weight as to be unsatisfactory from the viewpoint of practical properties.
In view of the above-mentioned situation, processes using a catalyst system comprising a titanium compound or a zirconium compound and an aluminum compound have hitherto been disclosed with the aim of solving these problems, and particularly in the recent time a process using a catalyst system comprising a titanium compound or a zirconium compound and an aluminoxane has been proposed.
However, the ethylene-.alpha.-olefin copolymer obtained with such a catalyst system is so low in molecular weight as to be unsatisfactory in practical properties.
On the other hand, as a process for polymerizing or copolymerizing an olefin by the use of a catalyst system comprising a compound having titanium-nitrogen bond and an organolauminum compound, the process of polymerizing ethylene by the use of a catalyst system comprising an organoaluminum compound and a solid component prepared by supporting a titanium amide compound or an alkali metal salt of titanium amide compound on magnesium halide (DE 2030753), the process of copolymerizing ethylene and an .alpha.-olefin by the use of a catalyst system comprising a titanium amide compound having pai-aryl ligand and an aluminoxane [Japanese Patent Application Kokai (Laid-Open) No. 87-121708], a process of polymerizing ethylene or copolymerizing ethylene and .alpha.-olefin by the use of a catalyst system comprising a titanium diphenylamide compound and an organoaluminum compound (EP 0104374), a process of copolymerizing .alpha.-olefin or ethylene and .alpha.-olefin by the use of a catalyst system comprising a titanium amide compound having aryl substituent and an organoaluminum compound (Japanese Patent Publication 67-22691), a process of homopolymerizing ethylene or .alpha.-olefin or copolymerizing ethylene and .alpha.-olefin by the use of a catalyst system comprising a titanium amide compound having a lower alkyl group such as diethylaminotitanium trichloride or the like and an organoaluminum compound [Japanese Patent Publication 66-5379; J. Polym. Sci. Part A-1, 241, 6 (1968)], a process of polymerizing ethylene by the use of a catalyst system comprising tetrakis(diphenylamido)titanium and an organoaluminum compound (Japanese Patent Publication 67-11646), etc. have been disclosed.
However, if ethylene and .alpha.-olefin are copolymerized by the use of the catalyst systems disclosed above, the following disadvantages arise. Thus, The Process of DE 2030753 is disadvantageous in that the resulting ethylene-.alpha.-olefin copolymer has a broad composition distribution. The process of Japanese Patent Application Kokai (Laid-Open) No. 87-121708 is disadvantageous in that the resulting copolymer has a low molecular weight. According to the processes disclosed in EP 0104374, Japanese Patent Publication 66-5379, Japanese Patent Publication 67-22691 and J. Polym. Sci. Part A-1, 241, 6 (1968), composition distribution of the resulting copolymer is yet unsatisfactory in the narrowness. The process disclosed in Japanese Patent Publication 67-11646 is yet unsatisfactory in the narrowness of resulting copolymer and catalyst activity. Further, if ethylene and .alpha.-olefin are copolymerized with this catalyst system, a polymer insoluble in solvent is formed at the time of polymerization which is entangled with stirring wheel of reactor. This is a fatal disadvantage from the viewpoint of continuous operation of the process.
On the other hand, as a process for producing .alpha.-olefin polymers by the use of an electron donor such as diketone compound, diester compound or the like, the process of producing .alpha.-olefin polymer by the use of a catalyst system comprising an organoaluminum and a solid catalyst composed of a titanium halide, an electron donor such as a diketone or diester compound and a magnesium halide is known, for example [Japanese Patent Application Kokai (Laid-Open) No. 82-151603]. However, if ethylene/.alpha.-olefin copolymerization is carried out with this catalyst system, the resulting copolymer is so broad in composition distribution that its practical properties are unsatisfactory.